If it does, you can take it and have two Viruses. For example, if you touch The Virus in the Treasure Room on Basement 1, and then you fight Lust in the Mini-Boss Room of Basement 2, Lust will still have the normal chance to drop The Virus. Set drops are not affected by item pools.Some specific collectible items are hard-coded to have a chance to drop from certain special events.However, in the actual game, Crawl Spaces draw from the Treasure Room pool. dungeon - Likely intended to be used for the Crawl Spaces.However, in the actual game, Challenge Rooms draw from the Treasure Room pool. challenge - Likely intended to be used for Challenge Rooms.However, in the actual game, the Boss Rush draws from the Treasure Room pool. bossrush - Likely intended to be used for the Boss Rush.In the itempools.xml file, we can see that there are some unused item pools: Seeing it in a Library and not touching it, however, allows it still to be encountered as a Treasure item, with slightly lowered weight. If the player sees Telepathy for Dummies in the Basement 1 Treasure Room, it is completely removed from all other pools for the rest of the run even without touching it.However, after the Treasure Map has already appeared twice on a run, it is completely decremented from the shop pool and it will never appear again. Thus, if you use a Restock Machine to reroll a Treasure Map, you have a chance for another Treasure Map to appear. All items in the shop pool are decremented by 0.5 on sight.(In this case, players do not have to touch the Notched Axe in order to prevent the game from ever spawning another one.) Thus, seeing a Notched Axe in the Basement 1 Treasure Room will make it impossible to see another Notched Axe in a future Treasure Room. All items in the Treasure Room pool are completely decremented on sight.The following item pools are decremented by 10% (0.1) on sight: Golden Chest and Greed Mode Golden Chest.The following item pools are decremented by 40% (0.4) on sight: The following item pools are decremented by 50% (0.5) on sight: Treasure Room and Greed Mode Treasure Room.The following item pools are fully decremented on sight: Touching an item will remove it from all item pools.If an item happens to be in more than one item pool, the weight decrementation will also apply to other pools.However, the amount of the decrementation varies depending on the specific item pool. When you see an item spawn, the weight of that item is automatically decremented inside of the respective item pool.Item weights were adjusted more extensively in Repentance.Plan C has a weight of 0.2 in the Curse Room, Devil Beggar, Devil Room, Greed Mode Shop, Red Chest and Shop pools, making it 80% less likely to encounter.Mega Blast has a weight of 0.2 in the Devil Room and Greed Mode Devil Room pools, making it 80% less likely to encounter.

Delirious has a weight of 0.4 in Angel Room pool, making it 60% less likely to encounter.

Bomber Boy has a weight of 0.2 in the Bomb Bum pool, making it 80% less likely to encounter.

Only a few items in the game do not have a weight of 1:.

((1 * 198) + (2 * 0.5) = 199) This means items with a weight of 1 have a 1 in 199 (0.5%) chance to spawn, while an item with a weight of 0.5 has a 1 in 398 (0.25%) chance to spawn. In a pool of 200 items that has only 2 items with a weight of 0.5, that would result in the total weight being 199.

However, if an item has a weight of 0.5, that means that item is 50% as likely to spawn compared to an item that has a weight of 1.

For example, if there are 200 items in a given item pool, and each item has a weight of 1, that means there is a 1 in 200 (0.5%) chance to get any particular item from that pool.

Nearly every item in the game has a weight of 1.

The weight represents how likely it is for the game to spawn the item.

Each item that is in an item pool has a weight associated with it.

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